Value cards or decrement cards are in widespread use worldwide. The cards are purchased by individuals from a card-issuing agency for use in telephones, vending machines, public transportation facilities and toll booths. They are in use, for example, in the Washington, D.C. subway system. The initial value of a given card is determined by the purchase price an individual pays for the card.
Access to goods and services, via a value card, is controlled by machines which accept, read, and verify the card. Upon completion of a transaction, the machine deducts the price from the value of the card by means of rewriting (and read-verifying) new card data leaving the process of card removal by the card owner. The owner can continue the use of the card until the value is exhausted.
Unfortunately, present value cards lack security because the cards are easily counterfeited or altered. Consequently, the use of magnetic stripe cards in the value card field has been limited to low denominations (i.e. under $100.00) where financial exposure is limited. In order for such cards to be used for higher denomination transactions higher degree of security is required.